The present disclosure relates generally to systems and methods for communications between a wireless device and a network and, more particularly, to systems and methods for coordinating communications during a wireless device changing between cells of a network.
As used herein, the term wireless device can refer to a variety of wireless devices such as mobile telephones, personal digital assistants (PDAs), handheld or laptop computers, and similar devices, including mobile stations (MS), user agent (UA), or user equipment (UE) that have telecommunications capabilities. In some embodiments, a wireless device may refer to a mobile, wireless device. The term wireless device may also refer to devices that have similar capabilities but that are not generally transportable, such as desktop computers, set-top boxes, or network nodes.
A wireless device may operate in a wireless communication network that provides high-speed data and/or voice communications. For example, the wireless device may operate in accordance with one or more of an Enhanced Universal Terrestrial Radio Access Network (E-UTRAN), Universal Terrestrial Radio Access Network (UTRAN), Global System for Mobile Communications (GSM) network, Evolution-Data Optimized (EV-DO), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), Integrated Digital Enhanced Network (iDEN), Universal Mobile Telecommunications System (UMTS), Enhanced Data rates for GSM Evolution (EDGE), GSM/EDGE Radio Access Network (GERAN) and General Packet Radio Service (GPRS) technology. Other wireless networks that wireless devices may operate in include but are not limited to Code Division Multiple Access (CDMA), cdma2000, cdma2000 1xRTT, cdma2000 HRPD, WLAN (e.g. IEEE 802.11) and WRAN (e.g. IEEE 802.22). wireless devices may also operate in fixed network environments such as, for example, Digital Subscriber Line (xDSL) environments, Data Over Cable Service Interface Specification (DOCSIS) cable networks, Wireless Personal Area Networks (PAN), Bluetooth, ZigBee, Wireless Metropolitan Area Networks (MAN) (e.g., WiMAX, IEEE 802.20, IEEE 802.22 Ethernet) or optical networks.
In wireless telecommunications systems, transmission equipment in a base station transmits signals throughout a geographical region known as a cell. Thus, each geographical region is serviced by a number of cells, often in an at least partially-overlapping arrangement. The process for deciding when and how a wireless device changes cells can be dictated by a number of variables, including specific communications technology utilized by the wireless device, the cells, and the overall network. For example, cells utilizing GERAN technology may utilize a variety of network control modes, including a purely autonomous (NC0) cell change mode, a partially autonomous (NC1) cell change mode, and a network controlled (NC2) cell change mode.
Regardless of the particular protocols utilized, while performing a “Cell Reselection,” there is typically a delay in packet data transfer, as some amount of time is used to perform switching and signaling operations in the new cell. In the case where a wireless device is in the process of a data transfer during a Cell Reselection, the delay can be readily appreciable by the user because the data transfer may be interrupted and delayed. This situation can be particularly prevalent because the network may assist or control the cell change, but is not aware of the amount of data that the wireless device wants to transmit. Based on the rough estimates, the network, depending upon protocol and implementation, can estimate the resource allocation desired by the wireless device to finish an in-process data transfer and, hence, delay the cell reselection process until the wireless device can complete the in-process data transfer. However, if the rough estimate by the network is incorrect or insufficient, there may still be a user-perceivable delay. This accuracy of the estimate may be very low because the network has very little information (especially at the entity such as the BSS which determines when to trigger cell change) on which to base its estimate.
For example, turning to FIGS. 1 and 2, this scenario can be readily illustrated. In particular, FIG. 1 is a schematic illustration of a wireless device 10 that is associated with a serving cell 12 and moving to a target cell 14. Also, FIG. 2 illustrates a sequence diagram for communications between a wireless device 10 and the network as the wireless device 10 “moves” from the serving cell 12 to the target cell 14. It is noted that a wireless device 10 may “move” from the serving cell 12 to the target cell 14 without a physical move. That is, the wireless device 10 may remain in the same location, yet change cells.
More particularly, FIG. 2 illustrates an example of a wireless device 10 and network implementing an NACC procedure in the case of 100 Radio Link Control (RLC) data blocks pending for transmission at the wireless device 10 side to the network when changing from communication through the serving cell 12 to the target cell 14 using a cell change notification (CCN) mode. In this example, the wireless device 10 is assigned 4 uplink (UL) timeslots and is using Modulation and Coding Scheme (MCS)-9 with RLC Acknowledged mode. It is noted that, for simplicity, Uplink Ack/Nack blocks from the network are not shown in FIG. 2. The transmission of these (and other control messages) may reduce the available resources for sending RLC data blocks.
In this situation, the wireless device 10 is under a good coverage of the serving cell 12, has established an Uplink temporary block flow (TBF) 16, and successfully transmitted an initial set of RLC data blocks 18. After that, the wireless device 10 determines that the cell reselection criteria 20 are met and successfully transmits “Packet Cell Change Notification” message 22 to the network through its connection in the serving cell 12. This Packet Cell Change Notification message 22 contains the current serving cell measurement and the identity of the proposed target cell 14. The wireless device 10 keeps transmitting uplink data 26 to the network through the serving cell 12 until the wireless device 10 receives system information applicable to the target cell 14 by means of one or more Packet Neighbour Cell Data messages 27 and “Packet Cell Change Continue” message 28 from the network. At this stage, the wireless device 10 suspends the TBF operation 30 in the serving cell 12 and performs the following sequence of steps: synchronizing with the target cell 14 frequency and frame boundaries and identifying the random access channels (RACH) and making a RACH Request 32; receiving an Immediate Assignment 34 and waiting for an allocated TBF starting time; at the TBF starting time, performing a “Packet Resource Request” 36, and optionally, receiving a “Packet Uplink Assignment” 38; and based on the allocated uplink state flag (USF) and temporary flow indicator (TFI), aborting the TBF at the serving cell 12 and starting a new TBF 40 with the target cell 14. In a congested cell and as per current 3GPP configuration, though unlikely, it is theoretically possible for the wireless device 10 to take up-to 10 seconds to achieve the actual transmission of the uplink data and complete transmitting the uplink data 42 or to determine that the cell change has failed and return to the previous serving cell. This amount of latency may be significantly visible to the end user, especially for a small data session like web browsing or sending an email.
Turning to FIG. 3, a similar data flow diagram to that of FIG. 2 is illustrated; however, this time the wireless device 10 and network are changing from communication through the serving cell 12 to the target cell 14 using a network ordered cell change (for example, in NC1 or NC2 mode). In this case, additional latencies may be observed during packet data transfer as, after the cell reselection, the wireless device 10 has to receive consistent system information set in the target cell 14 before triggering the two phase packet access procedure since in this example this information was not received while in the serving cell 12. Specifically, the wireless device 10 has established a TBF 16, successfully transmitted 27 RLC/MAC BSN 18, and sent Packet Measurement Report 44, before continuing with transmission of uplink data 46. However, when the wireless device 10 receiving a Packet Cell Change Order message 48, the wireless device 10 shall obey the Packet Cell Change Order irrespective of whether or not the wireless device 10 has any knowledge of the relative synchronization of the target cell 14 to the serving cell 12. Thus, the wireless device 10 suspends TBF and initiates cell reselection 50. As per the 3GPP specifications, the wireless device 10 must wait for the completion of the System Information Acquisition 52, which can theoretically last for up to T3174 (=15 s). Hence, in NCCC/NC2 mode it is possible to have a latency of up to 20 seconds (T3174+T3168) for the resumption of data transfer either in the new cell or (if the cell change is not successful) in the original cell.
The current solution in the 3GPP specification provides a limited estimate of wireless device resource requirement to the network by using the Countdown value (CV) transmitted in the RLC Data Blocks. It should also be noted that the CV value is only useful when the amount of data remaining in the buffer is very small; specifically, less than or equal to the number that would be transmitted within BS_CV_MAX radio block periods using the full uplink assignment of the mobile station. If more than this amount of data is to be transmitted, the CV value indicates a single value regardless of the amount of data. Because of this definition of the CV value, it is unlikely to be useful to indicate an amount of data that could be sent within the existing time limit for reselection. In particular, the BS_CV_MAX typically indicates the round-trip delay from wireless device to BSS and hence it is possible that such very small amounts of data would be sent anyway before the PCCC/PSHO/PCCO has been received by the wireless device.
Also, the wireless device informs the network about the uplink resource requirements using Packet Resource Request Message. But this message is transmitted by the wireless device when a different priority/different PFI based upper layer PDUs needs to be transmitted. For the data running with the same QoS and PFI, the Packet Resource Request may not be generated by the wireless device and, hence, the network will not be aware of the number of data bytes that the wireless device wants to transmit before the reselection procedure.
Thus, systems and methods that address the above-listed issues and allow the setting and the usage of optimal resource allocation for cell reselection would provide a useful improvement in the art.